308 METALLURGY OK CAST IRON.
so as to obtain the iron in the same state of heat and fluidity as when ordinary dry air at 62 degrees is used.
On the other hand, a higher temperature and greater dry ness of the atmosphere will operate in permitting the amount of fuel to be reduced.
In the above figures I have assumed ordinary conditions, but the actual practice must be carefully taken into consideration wherever it is desired to figure out the effects in any particular case, and it is well worth a foundryman's time to go into this question, figuring out the extra amounts of coke needed under various conditions of moisture and temperature, when a short observation of an ordinary hygrometer and thermometer will enable him to avoid the risk of cold and sluggish metal on any day.
Mr. W. H. Fryer has shown and published the statement* that air containing 0.8 per cent, of moisture will introduce about 89.6 pounds of water into a blast furnace per ton of iron made, using about 2,250 tons of coke for fuel. This is a factor the founder should not lose sight of. When air is moist, it is to some decree practically the same thing as fuel being water-logged. With very wet fuel, as many founders know, a larger percentage is necessary to re-melt iron than if the fuel were perfectly dry, and also that this can cause trouble much more readily in the line of ** bunging up " a cupola. For further information of the effects of humidity, see Chapters IX. and X.
* Journal of the Iron and Steel Institute, Vol. II., 1887. ratio of about 7.* iron fo i coke.